Esterified alkoxylated glycerin and other esterified alkoxylated polyols have recently been identified as useful reduced calorie fat substitutes. Compounds of this type, which are described more fully in U.S. Pat. No. 4,861,613, are substantially resistant to hydrolysis upon ingestion owing to the high proportion of linkages in which the carbons adjacent to oxygen in the fatty acid ester groups are secondary or tertiary in structure. In a preferred embodiment of such substances, the structure may be represented as follows: ##STR1## wherein G is a glyceryl radical, n is from about 1 to 5 on average, and R is a long chain paraffinic or olefinic hydrocarbon radical derived from a fatty acid.
However, the ability to use esterified alkoxylated polyols of this type at relatively high concentrations in food compositions is somewhat limited by the pronounced resistance of such substances to digestion. Since the esterified alkoxylated polyols are hydrolyzed and absorbed to only a very limited degree, the liquid versions of such substances tend to retain their oil-like physical characteristics after ingestion. Consumption of large amounts of these fat substitutes can result in leakage of the fat substitutes through the anal sphincter and separation of the fat substitute as an oil from the excreted fecal matter.
To enhance the acceptability of fat substitutes of this type, modified esterified alkoxylated glycerins have been developed which are somewhat less resistant to enzymatic hydrolysis than previously known esterified alkoxylated glycerins and yet still have significantly reduced calorie availability as compared to a conventional fully digestible triglyceride lipid. These modified esterified alkoxylated glycerins have at least one fatty acid acyl group attached directly to the glyceryl radical. These directly-attached acyl groups are readily hydrolyzed upon ingestion, rendering the compound less fat-like in character owing to the loss of one or two long-chain fatty acid acyl groups.
The other acyl groups in the esterified alkoxylated glycerin are attached to the glyceryl radical through oxyalkylene segments and thus are resistant towards enzymatic hydrolysis. Esterified alkoxylated monoglycerides and diglycerides of this type and their utility as reduced calorie fat mimetics are described more fully in European Patent Publication No. 481,523, incorporated herein by reference in its entirety.
The selective synthesis of esterified alkoxylated mono- and diglycerides is not straightforward. While procedures for obtaining such substances using ketal or benzyl protecting groups to selectively direct the addition of epoxide to the glycerin prior to esterification have been described, most notably in U.S. Pat. Nos. 5,118,448 and 5,135,683 (incorporated herein by reference in their entirety), such methods are not ideally suited for commercial purposes since in each instance separate steps are required for removal of the protective groups and esterification. For a fat substitute to penetrate the potential market for such food ingredients to the greatest extent, it must be capable of being produced at a minimum premium in cost over fully digestible vegetable and animal lipids. It is well-known that additional processing steps can significantly increase the expense of manufacturing food additives. Thus, a great need still exists for improved processes whereby an esterified alkoxylated glycerin having at least one acyl group attached directly to the glyceryl residue may be readily and economically prepared.